{"id":328,"date":"2024-04-22T00:10:37","date_gmt":"2024-04-21T16:10:37","guid":{"rendered":"https:\/\/cococat.top\/?p=328"},"modified":"2024-04-22T00:10:37","modified_gmt":"2024-04-21T16:10:37","slug":"rust-note-1-transmute","status":"publish","type":"post","link":"https:\/\/cococat.top\/index.php\/2024\/04\/22\/rust-note-1-transmute\/","title":{"rendered":"rust \u7b14\u8bb01: \u9ed1\u9b54\u6cd5\u4e4b std::mem::transmute"},"content":{"rendered":"

1. \u6458\u8981<\/h2>\n

\u5f53\u6211\u4eec\u5728\u5199\u5de5\u5382\u65b9\u6cd5\u65f6\uff0c\u6709\u65f6\u4f1a\u5e0c\u671b\u540c\u65f6\u8fd4\u56de\u4e24\u4e2a\u503c\uff1a\u4e00\u4e2a\u76ee\u6807\u5bf9\u8c61 + \u5bf9\u8be5\u5bf9\u8c61\u67d0\u4e2a\u6210\u5458\u7684\u5f15\u7528\u3002\u8fd9\u79cd\u8bbe\u8ba1\u521d\u542c\u8d77\u6765\u53ef\u80fd\u975e\u5e38\u4e0d\u5408\u7406\uff0c\u4f46\u662f\u5f53\u4f7f\u7528\u67d0\u4e9b\u5c01\u88c5\u4e0d\u592a\u5b8c\u7f8e\u7684\u7b2c\u4e09\u65b9\u5e93\u65f6\u662f\u53ef\u80fd\u51fa\u73b0\u7684\u3002\u4e3e\u4e2a\u4f8b\u5b50\uff1a\u6211\u4eec\u9700\u8981\u4e00\u4e2a\u5bf9\u8c61 A\uff08A \u7531\u7b2c\u4e09\u65b9\u5e93\u63d0\u4f9b\uff0c\u56e0\u800c\u65e0\u6cd5\u6539\u9020\uff09\uff0c\u800c\u53c8\u8981\u6784\u9020\u4e00\u4e2a\u5de5\u5177\u5bf9\u8c61 B\uff0c\u5176\u4e2d B \u53c8\u6301\u6709 A \u4e2d\u67d0\u4e2a\u6210\u5458\u7684\u5f15\u7528\u3002
\n\u663e\u7136\uff0cA \u548c B \u662f\u5f3a\u7ed1\u5b9a\u7684\u5171\u751f\u5173\u7cfb\uff0c\u56e0\u6b64\u6211\u4eec\u5e0c\u671b\u5c06 A \u548c B \u4fdd\u5b58\u5728\u540c\u4e00\u4e2a\u7c7b\u91cc\uff0c\u8ba9\u4ed6\u4eec\u7684\u751f\u547d\u5468\u671f\u540c\u6b65\u3002\u53ea\u8981\u6211\u4eec\u786e\u4fdd\u5b83\u4fe9\u4e00\u540c\u6784\u9020\u3001\u4e00\u540c\u9500\u6bc1\uff0c\u4e5f\u7edd\u4e0d\u4fee\u6539 B \u5f15\u7528\u7684\u6307\u5411\uff0c\u90a3\u4e48\u5185\u5b58\u5b89\u5168\u662f\u53ef\u4ee5\u5f97\u5230\u4fdd\u8bc1\u7684\u3002\u7136\u800c rust \u7f16\u8bd1\u5668\u4f1a\u963b\u6b62\u6211\u4eec\u8fd9\u4e48\u505a\uff0c\u8fd9\u662f\u56e0\u4e3a\u5176\u9884\u9632\u60ac\u5782\u5f15\u7528\u89c4\u5219\u7981\u6b62\u6211\u4eec\u6784\u5efa\u4e00\u4e2a\u53ef\u80fd\u6307\u5411\u65e0\u6548\u5bf9\u8c61\u7684\u5f15\u7528\uff0c\u5373\u7981\u6b62\u6301\u6709\u4e00\u4e2a\u4e34\u65f6\u5f15\u7528\u7684 B \u4f5c\u4e3a\u5de5\u5382\u65b9\u6cd5\u8fd4\u56de\u503c\u7684\u4e00\u90e8\u5206\u3002\u8fd9\u65f6\uff0c\u6211\u4eec\u9700\u8981\u60f3\u4e00\u4e9b\u529e\u6cd5\u6765\u7ed5\u5f00\u8fd9\u6761\u89c4\u5219\u3002
\n\u672c\u6587\u7ed9\u51fa\u4e86\u4e00\u79cd\u901a\u8fc7 unsafe<\/code> \u65b9\u6cd5 std::mem::transmute<\/code> \uff0c\u5f3a\u5236\u4fee\u6539\u5f15\u7528\u7684\u751f\u547d\u5468\u671f\uff0c\u4ece\u800c\u7ed5\u5f00\u7f16\u8bd1\u5668\u7684\u68c0\u67e5\u7684\u65b9\u6cd5 \u3002<\/p>\n

2. \u4e3e\u4e2a\u4f8b\u5b50<\/h2>\n

\u5bf9\u4e8e\u5f15\u7528\u5bf9\u8c61\uff0c\u6211\u4eec\u7528\u4e00\u4e2a\u7b80\u5355\u7684 struct<\/code> \u4f5c\u4e3a\u4f8b\u5b50\uff1a<\/p>\n

struct Referee(i64);\n\nimpl Referee {\n    fn get_mut(&mut self) -> &mut i64 {\n        &mut self.0\n    }\n}<\/code><\/pre>\n
\u4e4b\u524d\u63d0\u5230\uff0c\u53ea\u8981\u80fd\u4fdd\u8bc1\u5bf9\u8c61\u672c\u8eab\u548c\u5176\u90e8\u5206\u5f15\u7528\u540c\u6b65\u9500\u6bc1\uff08\u518d\u52a0\u4e0a\u907f\u514d\u4fee\u6539\u5f15\u7528\u6307\u5411\u5bf9\u8c61\uff09\uff0c\u5219\u7406\u8bba\u4e0a\u662f\u80fd\u786e\u4fdd\u5185\u5b58\u5b89\u5168\u7684\u3002\u56e0\u6b64\u6211\u4eec\u6784\u5efa\u4e00\u4e2a Bound<\/code> \u7c7b\uff0c\u5b58\u653e\u8fd9\u4e24\u4e2a\u6210\u5458\u3002\u4e3a\u4e86\u8ba9\u95ee\u9898\u7b80\u5355\u5316\uff0c\u6211\u4eec\u76f4\u63a5\u5c06\u53e6\u4e00\u4e2a\u6210\u5458\u8bbe\u8ba1\u6210\u5bf9 i64<\/code> \u7684\u5f15\u7528\uff0c\u5373\uff1a<\/p>\n
struct Bound<'a> {\n    reference: &'a i64,\n    inner: Referee,\n}<\/code><\/pre>\n
\u63a5\u4e0b\u6765\u5c31\u662f\u5de5\u5382\u65b9\u6cd5\u4e86\u3002\u5728\u4e0d\u8003\u8651 rust \u60ac\u5782\u5f15\u7528\u89c4\u5219\u65f6\uff0c\u6211\u4eec\u53ef\u80fd\u4f1a\u60f3\u8981\u8fd9\u4e48\u5199\uff1a<\/p>\n
fn create_bound<'a>() -> Bound<'a> {\n    let mut referee = Referee(666);\n    Bound {\n        reference: referee.get_mut(),\n        inner: referee,\n    }\n}\n<\/code><\/pre>\n
\u679c\u4e0d\u5176\u7136\uff0c\u7f16\u8bd1\u5668\u62a5\u9519\uff1a<\/p>\n
error[E0515]: cannot return value referencing local variable `referee`\n   --> src\/main.rs:113:5\n    |\n113 | \/     Bound {\n114 | |         reference: referee.get_mut(),\n    | |                    ------- `referee` is borrowed here\n115 | |         inner: referee,\n116 | |     }\n    | |_____^ returns a value referencing data owned by the current function\n<\/code><\/pre>\n
\u5bf9\u4e8e\u7edd\u5927\u591a\u6570\u60c5\u51b5\uff0c\u4e0a\u8ff0\u64cd\u4f5c\u786e\u5b9e\u4f1a\u4ea7\u751f\u60ac\u5782\u5f15\u7528\uff0c\u7f16\u8bd1\u5668\u7684\u62a5\u9519\u662f\u5408\u7406\u7684\u3002\u4f46\u5bf9\u4e8e\u8fd9\u4e2a\u7279\u6b8a\u7684\u573a\u666f\uff0c\u6211\u4eec\u4e5f\u65e0\u6cd5\u5bf9\u7f16\u8bd1\u5668\u8fdb\u884c\u89e3\u91ca\u6765\u8bf4\u670d\u5b83\u3002\u56e0\u6b64\uff0c\u4e3a\u4e86\u89e3\u51b3\u773c\u524d\u7684\u95ee\u9898\uff0c\u53ea\u80fd\u638f\u51fa unsafe \u6765\u50ac\u7720\u4e86\u3002\u4e00\u4e2a\u53ef\u884c\u7684\u5199\u6cd5\u662f\uff1a<\/p>\n
fn create_bound<'a>() -> Bound<'a> {\n    let mut referee = Referee(666);\n    Bound {\n        reference: unsafe { std::mem::transmute(referee.get_mut()) },\n        inner: referee,\n    }\n}\n<\/code><\/pre>\n
std::mem::transmute<\/code> \u53ef\u4ee5\u5c06\u4e00\u5757\u5185\u5b58\u5f3a\u5236\u89e3\u91ca\u6210\u53e6\u4e00\u79cd\u5bf9\u8c61\uff0c\u5373\u5b9e\u73b0\u65e0\u6761\u4ef6\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\uff0c\u7c7b\u4f3c\u4e8e C++ \u4e2d\u7684 reinterpret_cast<\/code> \u3002\u800c\u5728\u5f15\u5165\u4e86\u751f\u547d\u5468\u671f\u673a\u5236\u7684 rust \u4e2d\uff0ctransmute<\/code> \u4e0d\u4ec5\u80fd\u8f6c\u6362\u5bf9\u8c61\u7684\u7c7b\u578b\uff0c\u8fd8\u80fd\u5ef6\u957f\u6216\u7f29\u77ed\u5bf9\u8c61\u7684\u751f\u547d\u5468\u671f<\/strong>\u3002
\n\u5728\u4e0a\u8ff0\u4ee3\u7801\u4e2d\uff0c std::mem::transmute<\/code> \u7684\u4f5c\u7528\u6b63\u662f\u628a\u5176\u5185\u542b\u7684 referee.get_mut())<\/code> \u7684\u8fd4\u56de\u503c\u7684\u751f\u547d\u5468\u671f\u4ece\u5c40\u90e8\u53d8\u91cf\u5f3a\u5236\u8f6c\u6362\u4e3a\u4e0e\u8fd4\u56de\u503c\u4e00\u81f4\u7684 'a<\/code>\u3002<\/p>\n
3. \u8865\u5145\u4e4b\u4e00\uff1a'a<\/code> \u4e0d\u5982\u6539\u6210 'static<\/code>?<\/h2>\n
\u65e2\u7136\u5df2\u7ecf\u5728\u7528\u9ed1\u9b54\u6cd5\u4e86\uff0c\u90a3\u4e48 Bound<\/code> \u7c7b\u7684 'a<\/code> \u6807\u6ce8\u663e\u7136\u5df2\u7ecf\u5931\u53bb\u4e86\u610f\u4e49\u3002\u5012\u4e0d\u5982\u76f4\u63a5\u6539\u6210 'static<\/code>\uff0c\u8fd9\u6837\u4e5f\u80fd\u5f15\u5bfc\u4f7f\u7528\u8005\u4ea7\u751f\u7591\u95ee\uff0c\u8fdb\u800c\u53d1\u73b0\u8fd9\u6837\u5c01\u88c5\u7684\u9ad8\u5371\u6027\uff0c\u4ece\u800c\u7528\u7684\u66f4\u52a0\u8c28\u614e\u3002<\/p>\n
4. \u8865\u5145\u4e4b\u4e8c\uff1a\u4ece\u51e0\u884c\u4ee3\u7801\u770b rust \u6210\u5458\u6784\u5efa\u987a\u5e8f<\/h2>\n
\u5728\u521a\u521a\u7684\u4ee3\u7801\u6bb5\u91cc\uff0c\u5de5\u5382\u65b9\u6cd5 create_bound()<\/code> \u5728\u6784\u9020\u8fd4\u56de\u503c\u65f6\uff0c\u8fd9\u4e48\u5199\u662f\u6ca1\u95ee\u9898\u7684\uff1a<\/p>\n
    Bound {\n        reference: referee.get_mut(),\n        inner: referee,\n    }<\/code><\/pre>\n
\u4f46\u662f\u5982\u679c\u8fd9\u4e48\u5199\u5c31\u4e0d\u884c\u4e86\uff1a<\/p>\n
    Bound {\n        inner: referee,\n        reference: referee.get_mut(),\n    }<\/code><\/pre>\n
\u7f16\u8bd1\u5668\u62a5\u9519\u5185\u5bb9\u662f\uff1a<\/p>\n
error[E0382]: borrow of moved value: `referee`\n   --> src\/main.rs:106:49\n    |\n100 |     let mut referee = Referee(666);\n    |         ----------- move occurs because `referee` has type `Referee`, which does not implement the `Copy` trait\n...\n105 |         inner: referee,\n    |                ------- value moved here\n106 |         reference: unsafe { std::mem::transmute(referee.get_mut()) },\n    |                                                 ^^^^^^^ value borrowed here after move\n<\/code><\/pre>\n
\u53ef\u89c1\uff0crust \u5728\u6784\u9020\u5bf9\u8c61\u65f6\uff0c\u662f\u6309\u7167\u4ee3\u7801\u5199\u7684\u987a\u5e8f\u6765\u521d\u59cb\u5316\u5404\u4e2a\u6210\u5458\u7684\uff0c\u56e0\u6b64\u8fd9\u91cc\u5148 move \u4e86 referee \u4ee5\u540e\uff0c\u5c31\u4e0d\u80fd\u518d\u4f7f\u7528\u4e4b\u4e86\u3002\u8fd9\u4e2a\u6027\u8d28\u4e0e C++ \u7684\u6784\u9020\u51fd\u6570\u4e00\u5b9a\u6309\u7167\u7c7b\u578b\u5b9a\u4e49\u7684\u987a\u5e8f\u6765\u521d\u59cb\u5316\u6210\u5458\u4e0d\u4e00\u81f4\u3002\u5373\u5728 C++ \u4e2d\uff1a<\/p>\n
class MyClass {\npublic:\n    int a;\n    int b;\n\n    MyClass(int x, int y) : b(y), a(x) {}\n};<\/code><\/pre>\n
\u5373\u4f7f\u6211\u6784\u9020\u51fd\u6570\u7684\u521d\u59cb\u5316\u5217\u8868\u91cc\u5148\u5199\u4e86 b<\/code>\uff0c\u5b9e\u9645\u4e0a\u6700\u5148\u6784\u9020\u7684\u4f9d\u7136\u662f\u58f0\u660e\u987a\u5e8f\u4e2d\u7684 a<\/code><\/p>\n","protected":false},"excerpt":{"rendered":"
1. \u6458\u8981 \u5f53\u6211\u4eec\u5728\u5199\u5de5\u5382\u65b9\u6cd5\u65f6\uff0c\u6709\u65f6\u4f1a\u5e0c\u671b\u540c\u65f6\u8fd4\u56de\u4e24\u4e2a\u503c\uff1a\u4e00\u4e2a\u76ee\u6807\u5bf9\u8c61 + \u5bf9\u8be5\u5bf9\u8c61\u67d0\u4e2a\u6210\u5458\u7684\u5f15\u7528\u3002\u8fd9\u79cd\u8bbe\u8ba1 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-328","post","type-post","status-publish","format-standard","hentry","category-rust"],"_links":{"self":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/posts\/328","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/comments?post=328"}],"version-history":[{"count":0,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/posts\/328\/revisions"}],"wp:attachment":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/media?parent=328"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/categories?post=328"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/tags?post=328"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}